Human GLP-1 is a 37 amino acid residue peptide originating from preproglucagon which is synthesized i.a. in the L-cells in the distal ileum, in the pancreas and in the brain. GLP-1 is an important gut hormone with regulatory function in glucose metabolism and gastrointestinal secretion and metabolism. GLP-1 stimulates insulin secretion in a glucose-dependant manner, stimulates insulin biosynthesis, promotes beta cell rescue, decreases glucagon secretion, gastric emptying and food intake. Human GLP-1 is hydrolysed to GLP-1 (7-37) and GLP-1 (7-36)-amide which are both insulinotropic peptides. A simple system is used to describe fragments and analogues of this peptide. Thus, for example, [Gly8]GLP-1 (7-37) designates an analogue of GLP-1 (7-37) formally derived from GLP-1(7-37) by substituting the naturally occurring amino acid residue in position 8 (Ala) by Gly. Similarly, (Nε34-tetradecanoyl)[Lys34]GLP-1(7-37) designates GLP-1(7-37) wherein the ε-amino group of the Lys residue in position 34 has been tetradecanoylated.
In the last decade a number of peptides have been isolated from the venom of the Gila monster lizards (Heloderma suspectum and Heloderma horridum). Exendin-4 is a 39 amino acid residue peptide isolated from the venom of Heloderma suspectum, and this peptide shares 52% homology with GLP-1 (7-37) in the overlapping region. Exendin-4 is a potent GLP-1 receptor agonist which has been shown to stimulate insulin release and ensuing lowering of the blood glucose level when injected into dogs. The group of exendin-4(1-39), certain fragments thereof, analogs thereof and derivatives thereof, are potent insulinotropic agents.
A range of different approaches have been used for modifying the structure of glucagon-like peptide 1 (GLP-1) compounds in order to provide a longer duration of action in vivo.
WO 96/29342 discloses peptide hormone derivatives wherein the parent peptide hormone has been modified by introducing a lipophilic substituent in the C-terminal amino acid residue or in the N-terminal amino acid residue.
WO 98/08871 discloses GLP-1 derivatives wherein at least one amino acid residue of the parent peptide has a lipophilic substituent attached.
WO 99/43708 discloses GLP-1 (7-35) and GLP-1 (7-36) derivatives which have a lipophilic substituent attached to the C-terminal amino acid residue.
WO 00/34331 discloses acylated GLP-1 analogs.
WO 00/69911 discloses activated insulinotropic peptides to be injected into patients where they are supposed to react with blood components to form conjugates and thereby allegedly providing longer duration of action in vivo.
WO 02/46227 discloses GLP-1 and exendin-4 analogs fused to human serum albumin in order to extend in vivo half-life.
Many diabetes patients particularly in the type 2 diabetes segment are subject to so-called “needle-phobia”, i.e. a substantial fear of injecting themselves. In the type 2 diabetes segment most patients are treated with oral hypoglycaemic agents, and since GLP-1 compounds are expected to be the first injectable product these patients will be administered, the fear of injections may become a serious obstacle for the widespread use of the clinically very promising GLP-1 compounds. Thus, there is a need to develop new GLP-1 compounds which can be administered less than once daily, e.g. once every second or third day preferably once weekly, while retaining an acceptable clinical profile.